The present invention relates to a method for switching a drive of a hybrid vehicle from one operating mode to another operating mode, as well as to a hybrid vehicle for carrying out the method.
It is known that so-called “full-hybrid vehicles” are distinguished by a drive which has an internal-combustion engine and at least one propulsion-generating electric machine. A full-hybrid vehicle can be operated in different operating modes, which modes differ according to the “ratio of driving power generated by an electric motor to driving power generated by an internal-combustion engine”. The vehicle can, for example, be driven:                in a first operating mode, exclusively by an internal-combustion engine,        in a second (hybrid) operating mode, by an internal-combustion engine and simultaneously by an electric motor, or        in a third operating mode, exclusively by an electric motor.        
In the case of conventional hybrid concepts, it is possible for the driver to select a certain operating mode, such as “exclusively electric driving”, for example, by pressing a button provided in the instrument panel area or by selecting a corresponding function in a selection menu. If permitted by the momentary driving state and/or vehicle parameters (for example, vehicle velocity, charge state of the battery, etc.), the driver can actively, i.e. by himself, change to a certain operating mode. However, the pressing of a button and particularly the selecting of a function by way of a possibly relatively complex menu structure, require that the driver be highly observant, which can be problematic depending on the driving situation.
It is an object of the invention to provide a method for switching a hybrid drive from one operating mode to another operating mode, as well as a correspondingly developed hybrid vehicle, in which the change-over can be initiated by the driver as intuitively as possible.
The starting point of the invention is a hybrid vehicle having a drive which has an internal-combustion engine, at least one propulsion-generating electric machine and a transmission which can be shifted into different operating states by way of a “selecting device” to be actuated by a driver. The electric machine (motor) can particularly be designed such that an exclusively electric driving (i.e. without a combustion-engine drive) is also possible.
The hybrid drive can be operated in at least two, and preferably in at least three, different operating modes, for example:                as an “exclusive internal-combustion engine drive”,        as a “hybrid drive” (i.e. simultaneous internal-combustion engine drive and electric motor drive),        as an exclusive electric motor drive.        
The individual operating modes can be differentiated according to the “ratio of driving power generated by an electric motor to driving power generated by an internal-combustion engine”. Naturally, in the case of the exclusive internal-combustion engine drive mode, the fraction of the driving power generated by the electric motor will be zero. In the hybrid drive, the ratio of driving power generated by the electric motor to driving power generated by the internal-combustion engine may vary in a certain range. Naturally, in the case of an exclusively electric motor drive, the fraction of internal-combustion engine driving power will be zero.
The terms “operating mode” or “operating modes” should be interpreted very broadly. As an alternative to the above-described example, several different hybrid operating modes are, for example, also contemplated. Therefore, the at least two operating modes do not necessarily have to comprise an exclusively electric-motor driving mode or an exclusively internal-combustion engine driving mode.
The “drive” of such a hybrid vehicle has a plurality of control parameters (including marginal conditions), such as, for example, the power to be momentarily generated by the internal-combustion engine, the power to be momentarily generated by the electric machine, the power to be momentarily recuperated by the electric machine, the shifting state of the transmission etc. These control parameters are controlled by a drive control (one or more electronic control units having corresponding software programs).
Simply stated, the drive control controls the drive as a function of a “drive prompt” specified by the driver by way of:                the “accelerator element” (for example, the accelerator pedal) and        the transmission selecting device (for example, the gear selector lever or the gear selecting switch), and, as a function of different driving state and/or vehicle parameters or marginal conditions. The driving state parameters include, for example, the vehicle velocity and/or the charge state of the electric energy storage device (battery or capacitor arrangement) supplying the electric machine.        
In accordance with the invention, by activating an element already present in the vehicle anyhow, such as the selecting device (for example, the gear selecting switch or transmission selector lever), by which the transmission can be switched into its different operating states, the “drive” can very easily be actively switched by the driver from one operating mode (for example, the hybrid operating mode) to another operating mode (for example, the exclusively electric driving mode). The state selected by the driver or the shifting position of the selecting device selected by the driver therefore defines the momentary operating mode of the drive if permitted by the momentarily present driving state and/or vehicle parameters or marginal conditions.
Compared to conventional hybrid vehicles, where a switching from one operating mode to another operating mode takes place by way of a button or switch provided in the area of the instrument panel or at the steering wheel or by selecting a function from a software menu structure, a (mere) actuating of the selecting device, by which the individual operating positions of the transmission can also be selected, is absolutely also possible intuitively, while the driver can keep his eyes on the road. This novel difference from that of conventional hybrid vehicles is extremely advantageous ergonomically and has a direct positive effect on driver acceptance in the case of hybrid vehicles.
According to the invention, the drive is in a first operating mode when the selecting device is in a first (stable) state, and in a second operating mode when the selecting device is in a second (stable) state. The stable states may, for example, be defined shifting positions which a selector lever can assume, by way of which selector lever the transmission can be controlled.
It is explicitly pointed out that the invention provides or makes possible a switching-over between individual operating modes initiated by the driver which, however, does not exclude that, in certain situations, the drive control switches over automatically, i.e. without any action by the driver, from one operating mode to another operating mode.
In the case of a switching-over of the drive from one operating mode to another operating mode initiated by the drive control, for example, in the case of a switching-over from an exclusive electric-motor drive to a hybrid drive or to an exclusive internal-combustion drive, it may be provided that, in this case, the selecting device is also switched “automatically”, i.e. without any assistance by the driver. In this context, “automatic” means that the selecting device is shifted by the vehicle electronic system (drive control). From the shifting position of the selecting device and of a shifting noise possibly connected with the shifting of the selecting device, the driver therefore immediately receives a visual, haptic and/or acoustic acknowledgment concerning the (automatically implemented) change of the operating mode.
In addition, in the case of such a shifting operation, for example, in an instrument cluster, a change of the operating mode can be indicated by way of a display centrally arranged in the area of the instrument panel and/or by way of a so-called head-up display.
Furthermore, a visual status indication (for example, an LED or the like) may be provided at the selecting device (for example, at the selector lever) or in a different location in the driver's visual range, which indicates the momentarily selected operating mode.
An automatic switching from the exclusive internal-combustion engine drive to a hybrid mode or to an exclusive electric machine engine mode can be initiated by the driver, for example, by depressing the accelerator pedal (“kickdown”). A corresponding switching signal is supplied to the drive control. The drive control will then change the operating mode, which is accompanied by an automatic shifting of the selecting device or of the gear selector lever. If the driver's intention exceeds the exclusively electrically achievable maximum speed, it may also be provided that the exclusively electric driving mode is automatically exited.
As mentioned above, the selecting device may be a swivellably or tiltably arranged selector lever, similar to the selector lever found in the case of conventional vehicles with an automatic transmission of the BMW make. According to the present invention, such a selector lever can assume at least two stable states or selector lever positions. When the drive is in a first operating mode (for example, the hybrid operating mode), the selector lever is in an assigned first selector lever position. When the drive is in a second operating mode (for example, an exclusive electric motor drive), the selector lever is in a second selector lever position that differs from the first selector lever position.
It may further be provided that the selector lever can assume a third stable position, from which the transmission can be shifted in steps in a step shift gate into a higher or into a lower gear by actuating the selector lever.
Naturally, more than three stable selector lever positions may also be provided.
It may further be provided that a step-by-step shifting of the transmission by operating the selector lever from the position in which the drive is situated in an exclusive electric motor operating mode is impossible or is prevented.
When a certain operating mode (for example, an exclusive electric motor drive) is not possible in the case of the momentarily given driving state and/or vehicle parameters, it may be provided that the corresponding selection position is blocked; i.e., for example, that the selector lever cannot be moved into the position assigned to the corresponding operating mode.
As an alternative, an “earmarking” of the desired operating mode can be permitted, in that, although the selecting device can be moved into the corresponding selection position, a shifting into the desired operating mode is prevented as long as the momentarily given driving state and/or vehicle parameters do not yet allow it. Such an “earmarked state” may be displayed, for example, by a flashing of a status display (LED or the like). A change into the “earmarked operating mode” can then take place when this is permitted by the momentary driving state and/or vehicle parameters.
It may, for example, be provided that the three stable positions, which the selector lever can assume, are situated in a shift gate—viewed in the driving direction—one behind another or side-by-side (i.e. side-by-side being behind one another in the transverse direction of the vehicle). In this case, the selector lever, starting from the first stable position, which corresponds, for example, to a hybrid operating mode, by moving the selector lever in a first direction, can be shifted into another operating mode (for example, exclusive electric motor operation) and, by moving the selector lever in a second direction opposite the first direction or in a second direction perpendicular to the first direction, can be shifted into a third operating mode (sporty operation or exclusive internal-combustion engine drive).
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.